The present invention relates to a device for string instruments with a fingerboard, above which the strings are tensioned lengthwise and intended to be set into oscillation for tone generation, where the length of the strings"" oscillating part is variable for variation of pitch by pressing the string with a finger at selectable positions on the fingerboard, the strings running across a nut arranged at the upper end of the fingerboard across the fingerboard.
For string instruments of the above kind, difficulties exist with the accuracy of intonation across the different parts of the fingerboard. Furthermore, the strings have certain grades of stiffness, varying from one string to another, which often results in that an oscillation node does not appear exactly at the contact spot of the string against the fingerboard or fret. Particularly for new strings, this variability in stiffness creates a problem. This results in the tone being out of tune and the magnitude of the displacement of the oscillation node varies from one string to another and the location of the fingerboard and is impossible to foresee.
Certain string instruments of the aforementioned kind, for example, electric guitars and electric bases, are equipped with a mechanism at the string attachment on the bridge where one can vary the string length and thereby improve the intonation.
The purpose of the present invention is to provide a device for string instruments of the above-mentioned kind as well as such a string instrument that shows marked improvements in terms of accuracy of intonation.
This purpose is achieved with a device of the kind defined in the introductory portion having the characterizing features specified in claim 1 and with a string instrument specified in claim 13.
Because the nut includes several nut pieces that are arranged side by side over the width of the fingerboard and that are individually moveable in the lengthwise direction of the fingerboard, the distance between the contact spots of the strings on the bridge and on the nut will be adjustable allowing to improve the intonation.
According to an advantageous embodiment, an individually moveable nut piece is designed to carry each string. In this way, individual adjustment of each string is possible.
According to another advantageous embodiment of the device according to the invention, the nut pieces can be individually locked to the fingerboard by locking means, that are accessible between the strings for releasing for displacement and fixation of the nut pieces respectively. In this way, the locking means, which for example can be formed as screws, to screw the nut pieces onto the fingerboard, are easily accessible for release or fixation.
According to yet another advantageous embodiment of the invented device, a mechanism for varying the string length is mounted at the string attachment adjacent to the bridge. Through the co-operation between this mechanism and the moveable nut pieces, the whole oscillating part of the string can be moved lengthwise along the fingerboard, which makes it possible to obtain optimum intonation.
According to other advantageous embodiments of the invented device, said mechanism includes a swaying bridge with a holder within the instrument body, in which a rotating shaft is placed that is permeated by threaded screws, the lengths of which exceed the diameter of the shaft, and thus the screws extend beyond the shaft a certain distance, the strings being intended to be attached to the end of the projecting parts of the screws, which allows shifting of the pitch by turning of the threaded shaft. The length of the projecting part of the threaded screws is adjustable by turning the screw in the shaft. In this way, it is possible to achieve swaying and key changes in a simple way. Furthermore, it is possible to achieve swaying and key changes while preserving the tuning and the intonation. Strings at different diameters demand different amounts of slackening and tensioning for e.g. a half-note change, and as the projecting part of the screws are adjustable, the length of the projection can be adjusted to the size of the required change of the string length. A thin string demands more of slackening or tensioning than a thicker one.
According to yet another advantageous embodiment of the invented device, the rotating shaft is springs biased opposite to the direction that the strings normally strive to turn the shaft. In this way the tension from the strings will be balanced and allow for smooth turning of the shaft for swaying or key changes.
According to still another advantageous embodiment of the invention, the rotating shaft is arranged below a holder plate attached to the front side of the instrument, which holds rotating pins parallel to the front side of the instrument over which the strings are intended to run. Thus, when tensioning or slackening the strings, they will run smoothly over the breakpoint at the bridge without jamming.
According to other advantageous embodiments of the invented device the swaying area can be turned and locked into predetermined turning positions, whereby the distance between two predetermined turning positions corresponds to a predetermined change of pitch of the instrument. When turning the swaying area, it can suitably be moved along sticks positioned on the front side of the instrument body, locking rings being arranged in predetermined positions to keep the swaying area in desired position. The swaying area is thus locked against a certain ring, the position of the rings being arranged so that, for instance, locking of the swaying area against a first locking ring corresponds to a pitch change of a semitone, locking against the second locking ring a pitch change of a whole tone, and so on. In this way, it is possible to make a defined change of pitch of the whole instrument while playing can continue with the same fingering.
According to advantageous embodiments of the string instrument according to the invention frets are arranged across the fingerboard, at least some of them being curved to make it possible to improve intonation of the tone intervals. Preferably, the frets can be designed so that all thirds of the instrument will be pure.
According to still another advantageous embodiment of the instrument according to the invention, the frets are designed so that 19 tones per octave are available. This means a marked improvement of the intonation in comparison to today""s common tempered tuning with 12 tones per octave. Alternatively, the frets can be designed to make 31 tones per octave available. This is the perfect solution in terms of intonation.